1. Field of the Invention
The present invention relates to a projection device, a projection control method, and a storage medium, suitable for a projector or the like using a semiconductor light-emitting element as a light source.
2. Description of the Related Art
Recently, various kinds of projector devices, which employ semiconductor light-emitting elements, such as a light-emitting diode (LED) or a semiconductor laser (LD), as light sources, have been commercialized. In such kinds of projector devices, a semiconductor element, which directly emits G light with a light amount substantially equal to the light amount of each of R light and B light, among R (red) light, G (green) light and B (blue) light of the three primary colors, has not yet been put to practical use. Under the circumstances, B light, which is emitted from an LD, is radiated onto a phosphor wheel that is coated with a phosphor, and G light obtained from the phosphor is collected and utilized.
The above-described phosphor wheel is configured such that a part of a plate surface, on which B light is radiated, is formed as a fan-shaped transmissive diffusion layer, and the other part is formed as an opaque phosphor layer. By the rotation of the phosphor wheel, B light, which has passed through the transmissive diffusion layer, and G light, which has been collected from the phosphor layer, can be utilized in a time-division manner.
A projection device using the above-described semiconductor light-emitting element is also disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 2014-164289.
FIG. 4 is a view illustrating a general activation sequence of a projector device using a semiconductor light-emitting element. Part (A) of FIG. 4 illustrates a detection pulse CWINDEX from a marker sensor that is provided to be opposed to a marker for synchronism detection which is attached to a circumferential surface of a phosphor wheel. Part (B) of FIG. 4 illustrates a turn-on pulse LD-ENBL which permits light emission of an LD that is a light-emitting element. Part (C) of FIG. 4 illustrates a current setting signal for setting a driving current of the LD.
At a time of activating the projection device, the current setting signal shown in part (C) of FIG. 4 is first turned on, thereby starting supply of power to the LD. Then, the phosphor wheel is rotated, and the detection pulse CWINDEX is obtained as shown in part (A) of FIG. 4.
Thereafter, as shown in part (B) of FIG. 4, at a timing t11, the turn-on pulse LD-ENBL is delivered to the LD. Thereby, since the current setting signal is already turned on, light emission is executed in accordance with this turn-on pulse, and a projection operation is started. Subsequently, at a timing t12, a search for an input signal is started. Thereby, if an input signal is delivered, the projection of video corresponding to this input signal is started.
In this activation sequence, as indicated by a broken-line area A11 in FIG. 4, since the turn-on pulse is output immediately after starting the rotation of the phosphor wheel, the projection operation is started before the phosphor wheel and the light emission of the LD are correctly synchronized. Consequently, such a problem arises that flickering occurs in the projected content.
In order to solve this problem, a method as illustrated in FIG. 5 is thinkable. In this method, the output of the turn-on pulse to the LD is delayed by a fixed time, for example, one second to two seconds, from the start of the rotation of the phosphor wheel. Thereby, in the state in which the rotation of the phosphor wheel is stabilized, the LD is correctly synchronized and driven to emit light.
In the activation method illustrated in FIG. 5, flickering of video can be suppressed by delaying the output of the turn-on pulse to the LD by the fixed time. However, since the start of the projection operation is delayed by that time, the advantage of the light source, for which the semiconductor light-emitting element that can immediately start projection after activation is used, would be lost.
Accordingly, it is an object of the invention to provide a projection device, a projection control method, and a program, capable of starting projection in a short time without causing flickering to occur.